1. Field of the Invention
The present invention relates to an optical coupling device having a function of electrically isolating an input side and an output side from each other by converting an electrical signal into an optical signal by means of a light emitting device and converting the optical signal back into the electrical signal by means of a light receiving device.
2. Description of the Related Art
An opposed-type optical coupling device in which a light emitting device and a light receiving device are arranged to oppose each other is known in the art. FIG. 20 illustrates an optical coupling device 2000 having such a structure. The optical coupling device 2000 includes a light emitting device 1 and a light receiving device 2 which are mounted on header sections of respective lead frames 14. The light emitting device 1 and the light receiving device 2 are wire-bonded to the respective lead frames 14 via gold wire 3. The light emitting device 1, the light receiving device 2 and the lead frames 14 are molded together with a light transmissive resin 5 into a rectangular parallelepiped shape. The rectangular parallelepiped structure is further molded in a light blocking resin 16. Thus, the resulting device has a double-molded structure.
FIG. 21 illustrates a structure of another opposed-type optical coupling device 2100 known in the art. In the optical coupling device 2100, substantially U-shaped insulative substrates 2106A and 2106B are used instead of the lead frames 14. The light emitting device 1 and the light receiving device 2 are placed respectively in the substantially U-shaped insulative substrate 2106A on the light emitting side and the substantially U-shaped insulative substrate 2106B on the light receiving side. The two substantially U-shaped insulative substrates 2106A and 2106B are attached together so that the devices 1 and 2, opposing each other, are optically coupled together. Wiring patterns 2104A and 2104B are provided on the insulative substrates 2106A and 2106B for the devices 1 and 2, respectively. In FIG. 21, a line 2104C running substantially through the center of the optical coupling device 2100 denotes an adhesive with which the insulative substrates 2106A and 2106B are attached together.
FIG. 22 illustrates a structure of still another optical coupling device 2200 using insulative substrates. The optical coupling device 2200 includes a substantially U-shaped insulative substrate 2206A and a plate-like insulative substrate 2206B. Wiring patterns 2204A and 2204B are provided on the substantially U-shaped insulative substrate 2206A, and a wiring pattern 2204C is provided on the plate-like insulative substrate 2206B. The wiring pattern 2204A extends from an area of the substantially U-shaped insulative substrate 2206A on which the light emitting device 1 is mounted to the outside of the optical coupling device 2200, where the wiring pattern 2204A functions as a soldering section. The wiring pattern 2204B extends from the bottom of one end of the plate-like insulative substrate 2206B to the outside of the optical coupling device 2200, where the wiring pattern 2204B functions as a soldering section. The wiring pattern 2204C extends from an area of the plate-like insulative substrate 2206B where the light receiving device 2 is mounted to the bottom of one side surface of the plate-like insulative substrate 2206B. The plate-like insulative substrate 2206B is structurally connected to the wiring patterns 2204A and 2204B via solder bumps 2208A and 2208B. The solder bump 2208B electrically connects the wiring pattern 2204C to the wiring pattern 2204B.
However, when a lead frame is used in an opposed-type optical coupling device, the following problems arise. The thickness of a lead frame is 0.2 mm at minimum. For the light emitting side and the light receiving side in combination, a total thickness of 0.4 mm is required for the lead section, whereby it is difficult to reduce the overall thickness of the optical coupling device. For example, in the conventional example illustrated in FIG. 20, which employs the double-molded structure, the thickness of the optical coupling device 2000 is currently 2.1 mm at minimum.
Moreover, in the optical coupling device 2000, an electrical signal is first transferred to the light emitting side lead frame 14 and then to the light emitting device 1 mounted on the header section of the light emitting side lead frame 14. The electrical signal is converted into an optical signal at the junction plane 1A of the light emitting device 1, and then propagated to the light receiving device 2. The optical signal which has been emitted from the junction plane 1A of the light emitting device 1 toward a side surface thereof is absorbed by the light transmissive resin 5, whereby substantially no portion of the optical signal reaches the light receiving device 2. Moreover, substantially all of the optical signal which has reached the periphery of the light transmissive resin 5 is absorbed by the light blocking resin 16 and thus is not propagated to the light receiving device 2. Thus, the transmission efficiency is poor in this conventional example.
The conventional example illustrated in FIG. 21, which does not use a lead frame, is quite useful in reducing the overall thickness of the optical coupling device. However, in this structure, it is difficult to solder the wiring patterns 2104A and 2104B to the insulative substrates 2106A and 2106B, respectively, thereby complicating the production process. Moreover, the devices 1 and 2 are mounted in the substantially U-shaped insulative substrates 2106A and 2106B, respectively, which makes the die-bonding or wire-bonding process more difficult.
The conventional example illustrated in FIG. 22 is also quite useful in reducing the overall thickness of the optical coupling device. However, it is necessary to make an electrical connection between the wiring pattern 2204C of the upper, plate-like insulative substrate 2206B and the wiring pattern 2204Bon the lower, substantially U-shaped insulative substrate 2206A, thereby complicating the production process. Moreover, since the devices are mounted in the lower, substantially U-shaped insulative substrate 2206A, which makes the die-bonding or wire-bonding process more difficult.
According to one aspect of this invention, there is provided an optical coupling device, including: a light emitting device for converting an electric signal into an optical signal and outputting the optical signal; and a light receiving device for receiving the optical signal output from the light emitting device and converting the optical signal into the electric signal, wherein: the light emitting device has a light emitting surface for outputting the optical signal; the light receiving device has a light receiving surface for receiving the optical signal; and the light emitting device and the light receiving device are arranged so that the light emitting surface and the light receiving surface oppose each other, the optical coupling device further including: a first insulative substrate on which the light emitting device is mounted; and a second insulative substrate on which the light receiving device is mounted, wherein: the first insulative substrate has a first cross section; and the second insulative substrate has a second cross section; and at least one of the first cross section and the second cross section is substantially L-shaped.
In one embodiment of the invention, the first insulative substrate has a wiring pattern connected to the light emitting device; and the wiring pattern includes a soldering terminal section.
In one embodiment of the invention, the light emitting device is connected to the wiring pattern by way of wire bonding.
In one embodiment of the invention, the second insulative substrate has a wiring pattern connected to the light receiving device; and the wiring pattern includes a soldering terminal section.
In one embodiment of the invention, the light receiving device is connected to the wiring pattern by way of wire bonding.
In one embodiment of the invention, the soldering terminal section is provided on an opposite side from a leg of the substantially L-shaped cross section with respect to the light receiving device.
In one embodiment of the invention, the first insulative substrate and the second insulative substrate are molded together with a light blocking resin.
In one embodiment of the invention, the light blocking resin includes an epoxy resin.
In one embodiment of the invention, at least one of the first insulative substrate and the second insulative substrate has a protrusion which is provided along an edge of a device mount surface on which either the light emitting device or the light receiving device is mounted, the protrusion being substantially perpendicular to the device mount surface; and a side surface of the protrusion is in contact with an inner surface of the other insulative substrate.
In one embodiment of the invention, the first insulative substrate has a slope portion for reflecting the optical signal output from the light emitting device toward the light receiving device.
In one embodiment of the invention, the optical signal which has been emitted toward a side surface of the light emitting device is reflected by the slope portion toward the light receiving device.
In one embodiment of the invention, the first insulative substrate has a through hole; the first insulative substrate has a wiring pattern connected to the light emitting device; and the wiring pattern extends from an inner surface of the first insulative substrate via the through hole to an outer surface of the first insulative substrate.
In one embodiment of the invention, the second insulative substrate has a through hole: the second insulative substrate has a wiring pattern connected to the light receiving device; and the wiring pattern extends from an inner surface of the second insulative substrate via the through hole to an outer surface of the second insulative substrate.
In one embodiment of the invention, the optical coupling device further includes a light transmissive resin filled the first insulative substrate and the second insulative substrate.
In one embodiment of the invention, the light transmissive resin includes a silicone resin.
The present invention provides an opposed-type optical coupling device which employs an insulative substrate having a wiring pattern provided by plating, or the like, as a substrate on which a light emitting device and a light receiving device are mounted. In this way, it is possible to eliminate the need to use thick lead frames, thereby significantly reducing the overall thickness of the device. Moreover, the substantially L-shaped cross section of the insulative substrate facilitates the die-bonding or wire-bonding process as compared with the case where a substantially U-shaped insulative substrate as in the prior art.
Moreover, the light emitting device side insulative substrate can be provided with a light emitting side soldering terminal section (electrode), and the light receiving device side insulative substrate can be provided with a light receiving side soldering terminal section (electrode). Therefore, it is possible to eliminate the need to connect the wiring pattern on the upper substrate to the wiring pattern on the lower substrate, as in the prior art, thereby significantly improving the productivity.
The light emitting device side insulative substrate and the light receiving device side insulative substrate can be molded together with a light blocking resin. Particularly, when the junction between the light emitting device and the light receiving device has a complicated configuration, the resin molding improves the productivity. Using an adhesive can further stabilize the product quality.
Furthermore, a protrusion may be provided at the tip of the device mount surface of a substantially L-shaped structure of one insulative substrate, so that the protrusion extends in a direction substantially perpendicular to the device mount surface and that a side surface of the protrusion is in contact with an inner side surface of the other insulative substrate. In this way, it is possible to increase the creepage distance along the boundary between the periphery of the light transmissive resin structure and the inner surface of the insulative substrates, thereby increasing the withstand voltage of the optical coupling device. This is because when a high voltage is applied between the light emitting side and the light receiving side, a discharge, if any, would occur in a location where the withstand voltage is lowest, and such a location (within the optical coupling device itself excluding the ambient space) corresponds to the boundary between the periphery of the light blocking resin structure and the inner surface of the insulative substrates.
The leg (herein, the term xe2x80x9clegxe2x80x9d is used to refer to the shorter one of the two linear segments of the substantially L-shaped configuration) of the substantially L-shaped cross section of the lower insulative substrate may be provided opposite from the soldering terminal section with respect to the device. In this way, it is possible to increase the creepage distance along the boundary between the periphery of the light transmissive resin structure and the inner surface of the insulative substrates, thereby increasing the withstand voltage of the optical coupling device.
The light receiving device side insulative substrate may be provided with a slope portion so that the optical signal which has been emitted toward a side surface of the light emitting device is reflected by the slope portion toward the light receiving device. In this way, it is possible to significantly improve the optical transmission efficiency.
Moreover, the insulative substrate may be provided with a through hole so that the wiring pattern can extend from the inner surface of the insulative substrate through the through hole to the outside of the optical coupling device. In this way, it is possible to increase the creepage distance along the boundary between the periphery of the light transmissive resin structure and the inner surface of the insulative substrates, i.e., the distance along such a boundary between the electrically active portion on the light emitting side and the electrically active portion on the light receiving side. Herein, the term xe2x80x9celectrically active portionxe2x80x9d is used to mean any portion of the light emitting side or the light receiving side which is electrically connected to the terminal of the light emitting side or the light receiving side, respectively. In the present specification, the term xe2x80x9celectrically active portionxe2x80x9d is used to refer to the wiring pattern itself.
Thus, the invention described herein makes possible the advantages of: (1) providing an optical coupling device capable which can be produced with a reduced thickness and an improved productivity, and in which the optical transmission efficiency can be improved.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.